The invention relates to eddy current probes for inspecting long tubular members and more particularly to bobbin probes that are attached to the ends of flexible conduits for inspecting tubes at high speeds.
Eddy current probes are employed to inspect small (about three quarter of an inch or smaller) tubes of tube bundles of shell and tube heat exchangers having hundreds or even thousands of tubes and the like. In a commercial application of particular concern to the inventors, the tube bundles are U-tubes extending from a tube sheet of steam generators of the type manufactured by the assignee of the present invention for use in commercial nuclear power plants for generating electricity. The U-tubes of such heat exchangers may extend for thirty feet or more from their tube sheets. To inspect the tubes of such steam generators, an elongated probe attached to the end of a long section of flexible delivery conduit is robotically introduced into a tube, moved through the tube at relatively high speeds to inspect the straight and bend portions, withdrawn from the tube and then introduced into another tube in the tube bundle. Bobbin probes are frequently employed because these probes can provide accurate indications of cracking, corrosion and other flaws. These inspections are generally conducted on critical path schedules so that they must be accurately conducted at high speeds. U.S. Pat. No. 5,279,168 discloses a bobbin probe assembly that may be employed to inspect U-tubes of steam generators. Other eddy current probe assemblies are disclosed in the following U.S. Pat. Nos.: 4,438,399; 4,889,679; 4,668,912; 4,683,361; 4,856,337; 5,105,876; 5,134,367; 5,247,251. These patents, including U.S. Pat. No. 5,279,168, are hereby incorporated for their disclosures of the structures and uses of eddy current probes for testing tubing.
The majority of failures of bobbin probes used commercially are in the heads of the probes rather than in their flexible delivery conduits. Thus, the art has developed replaceable heads in order to eliminate the cost of having to replace the entire probe and delivery conduit and to reduce the probe change out time. As is shown by the U.S. Pat. No. 4,438,399, these heads may have bayonet coupling designs (or xe2x80x9cJxe2x80x9d locks) for readily changing probes. However, these couplings may detach when subjected to high speed pulling and pushing forces and twisting in the tight inner rows of the inner tubes of the U-tube bundles.
It is an object of the present invention to provide a bobbin probe head having a more rugged quick release coupling. It is a further object to provide a bobbin probe head that will not detach from a flexible delivery conduit during high speed pulling and pushing in the tight inner bends of U-tubes.
With these objects in view, the present invention resides in an eddy current testing probe for releasably coupling with a delivery conduit. The probe has a head portion with bobbin coils and a delivery conduit connector portion, with a flexible conduit having a first end extending from the head portion to a second end extending to the connector portion. The connector portion has electrical terminal connections electrically connected to the bobbin coils by wires extending through the flexible conduit and has a housing with a surface surrounding the electrical terminal connections. Importantly, the housing surface surrounding the electrical terminal connections has a 360xc2x0 delivery conduit mechanical interlock. The interlock may in one embodiment of the present invention be a recess for receiving a proturburance on the delivery conduit or may in a second embodiment be a proturburance for engaging a recess in the delivery conduit. Advantageously, a interlock provides a circumferential mechanical lock which will not readily disengage when a probe and its delivery conduit move and twist at high speeds through small tubes and around tight bends of U-tubes.